Disk drive memory systems store digital information on magnetic disks. The information is stored in concentric tracks divided into sectors. The disks themselves are rotatably mounted on a spindle, and information is accessed by means of read/write heads mounted on pivoting arms able to move radially over the surface of the disk. This radial movement of the transducer heads allows different tracks to be accessed. Rotation of the disk allows the read/write head to access different sectors on the disk.
In operation, the disk or disks comprising the magnetic media are rotated at very high speeds by means of an electric motor generally located inside the hub that supports the individual disks. Bearings mounted inside the hub allow the hub to rotate about a fixed shaft. These bearings are typically ball bearings or fluid bearings. Bearings having a fluid lubricant are desirable for disk drive applications because of their inherently low, nonrepeatable run out and low acoustic noise. However, these bearings suffer from several shortcomings. For instance, the oil used to provide the fluid bearing has a tendency to leak and outgas. Therefore, such bearings may lead to contamination of the interior of the disk drive. Such contamination may cause a failure of the drive in the form of data errors. Bearing systems incorporating an oil lubricant also have a limited maximum rotational speed due to their large power consumption at high speeds.
Alternative designs have utilized air bearings having grooved surfaces to generate areas of increased pressure when the surfaces of the bearing move in opposition to each other. However, such designs have typically had only a unidirectional thrust mechanism, and therefore the disk drive can only be operated when the device is in certain orientations (e.g. upright), or the device cannot withstand shock in certain directions (e.g. the axial direction). Furthermore, previous designs have featured relatively small-diameter radial bearing surfaces, resulting in bearings that have inadequate stiffness. Therefore, conventional air bearing designs result in a bearing that cannot maintain the rotating components in a precise relationship to the stationary components when bearings constructed in accordance with those designs are subjected to external forces. Adequate stiffness is difficult to achieve in an air bearing because air has a viscosity that is much lower than the viscosity of oil or other conventional lubricants.
Other bearing designs have utilized pressurized gas as a lubricating fluid. Such designs require an external supply of pressurized air and so would not be suitable for a disk drive application.
Air is desirable as a bearing lubricant because its use removes concerns about leakage and outgassing. In addition, the viscosity of air does not vary with changes in temperature as much as does the viscosity of oil or other lubricants. Furthermore, air bearings provide lower acoustical noise characteristics and less non-repeatable run out than ball-bearing designs and lower power consumption due to decreased friction than oil-filled bearings. However, known designs using air as a lubricant have used extremely high rotational speeds or extremely tight internal clearances or both to increase the stiffness of the bearing in order to achieve stiffness levels that are comparable to the stiffness of oil filled bearings. A bearing that lacks stiffness will allow the rotating disks to deviate from the desired alignment when the drive is subjected to external forces. High rotational speeds and tight clearances have been necessary in conventional air bearings because the viscosity of air is approximately 1/700 that of oil. However, increased rotational speeds generally reduce the storage capacity of the disk drive because of limitations in read/write channel data rates. Also, the tight internal clearances typically employed by known air-bearing designs increase manufacturing costs tremendously.
Other air bearing designs are physically larger in size than conventional oil filled bearings, and are therefore unsuitable for small form factor drives. Also, these other designs have a relatively large number of parts, increasing manufacturing costs.
It would be desirable to provide a bearing system for a disk drive motor assembly that utilized air as the fluid medium between bearing surfaces. In addition, it would be desirable that such a device be easy to manufacture in large volumes and at low cost. Furthermore, it would be advantageous to provide a bearing having adequate stiffness, while providing enhanced performance, lowered power consumption and wear and tear, and having a longer life than conventional bearings.